Sublimation process



Au M, mm. I flAMfii-k C. R. DOWNS SUBLIMATION PROCESS Filed July 2, 1919 INVENTOR l til CHARLES E. 'DGS, F CLIFFSIDE, NEW JERSEY, ASSIGNOR TO THE BARRETT GQMP, A CORPORATION OF NEW JERSEY.

SUBLIMATION PROCESS.

Application filed July 2,

To all whom it may concern Be it known that I, CHARLES R.-Dow1ys, a citizen of the United States, residing at Cliffside, in the county of Ber on and State of New Jersey, have invente certain new and useful Improvements in Sublimation Processes, of which the following is a speci-,

fication. I

This invention relates to a process of purifying materials that can be readily sublimed. By this invention a mixture of two or more of such materials may be separated into fractions, each one of which fractions may consist of a compound'that is relatively or entirely free from the presence of other compounds. The process has proven most satisfactory in the treatment of mixtures of materials which sublime at widely different temperatures and do not ha]ve the property of forming mixed crysta s.

The invention will be specifically described in connection with the purification of anthraquinone and also in connection with the purification of phthalic acid anhydride but it is to be understood that the invention is not restricted to the treatment of these particular materials. .Other materials having properties similar to the ones in connection with which the invention will be described may be successfully treated according to this invention with satisfactory results.

By using the old and well-known methods for producing anthraquinone-by the o'x'idar from the waste chromate liquors, dried'and heated in avessel while super-heated steam is referably blown :throu hthe mass in onfer to assist the sublimation of the anthraquinone. The anthraquinone vapor mixed with the steam is then carried into a receiving chamber where the condensable materials are condensed by means of a spray of water. A screen in the bottom of the container catches the crystals and permits the surplus liquid to drain oil". It is then necessary to dry the crystals before they can 1919. Serial No. 303,308.

be further used, for example, for sulfonatmg the same to produce alizarine. The crystals of anthraquinone produced in this way are exceedingly light and fiufiy so that they occupy a very large volume and are so light that caremust be taken in order to prevent loss of the same by being carried away by gusts of air. Also impurities or other by-products condensed from the vapors are mixed with the anthraquinone crystals- For example, unoxidized anthracene is apt to be mixed in somewhat large percentages with the anthraquino'ne.

When naphthalene is oxidized to produce phthalic acid, the same sorts of cliiiiculties are experienced as by-products or impurities are carried along with the vapors and condensed and become mixed with the phthalic acid anhydride crystals, At the same time the phthalic acid crystals are very small, consequently requiring care in handling to prevent loss of the same.

Recently, processes have been developed by which anthracene and naphthalene can be oxidized in the vapor phase by means of an oxygen containing gas in the presence of suitable catalyzers so as to produce large yields of anthraquinone and phthalic acid anhydride, respectively. In'these processes as practiced at present appreciable amounts of by-products are also formed as in the old processes, which 'by-products are found mixed with the final product and render the same impure By-this invention the difliculties and objections of prior processes are largely overcome and compounds are produced, usually in large crystals, which are relatively free from the presence ofobjectionable impurities. In practicing this invention the-impure material, such as anthraquinone or phthalic acid or,anhydride, or other materials, are first vaporized and the vapors are condensed-s0 that large crystals ofcomparative purity may be directly obtained from the Vapors. The vapors from the materials treated may be carried by means of air or a neutral gas into a container having separate compartments which are maintained at difi'erent temperatures so that a portion of the vapors consisting largely or'en'tirely of one compound is condensed in one chambar and another portion is condensed in another chamber maintained at a difi'erent temperature.

- tion it was found that in the purification of In the practice of this invention the crude product to be purified is sprayed in a melted condition into a chamber maintained at a predetermined temperature where it is met by and intimately mixed with a stream of a neutral, fixed gas which has been preheated'to the same temperature. This gas then becomes saturated with the vapors of the compound which is to be produced in a pure condition. These vapors then pass into a zone which is held at such a temperature that the gas is slightly supersaturated with thevapors of one of the compounds whereby fractional condensation takes place and this compound crystallizes from the vapor form in large pure crystals. The residual mixed gas and vapors then pass onto a zone whose temperature is still lower and again the gas becomes supeisaturated with the vapors of the compounds and further crystals result. To obtain an optimum separation of impurities from thematerial desired, it is advisable to construct the fractional condenser ith a large number of Zones wherein the temperature gradient. drops slowly from the entrance to the outlet.

A specific illustration of the invention is by the sublimation of impure anthraquinone containing some anthracene and phthalic acid. The impure material is sprayed into a chamber at a tempreature of from 280 C. to 300 C. and there mixed with a stream of hot air. The mixed vapors then pass into the first compartment held at bout 200 G. Large needle like crystals of anthraquinone as much as 2 inches in length are obtained with a purity of at least 99% and free fro-m phthalic acid. The vapors then pass through other compartments of successively lower temperatures and substantially pure anthraquinone separates because the gases are supersaturated with the vapors of anthraquinone at that temperature and not with the vapors of anthracene and phthalic anhydride. In the later compartments mixtures of phthalic anhydride and anthracene containing some anthraquinone are deposited which may be rerun to regain a large proportion of the anthraquinone or may be purified by well known chemical means.

As a further illustration of this invenphthalic acid anhydride by this process, commercial phthalic acid containing benzoic acid, maleic acid, naphthaquinone and naphthalene was vaporized and the vapors treated in a manner similar to that above described in connection with anthraquinone. While operating with phthalic acid (or phthalic acid anhydride) the temperature of vaporization was held at about 200 C. and the temperature of the first chamber was maintained at about 94 C. Crystals of phthalic acid anhydride were obtained about gas.

a foot in length practically free from the presence of by-products or other impurities.

An apparatus which has proven successful in the practice of this process is illustrated in the accompanying drawing which is a View partly in section. Other apparatus may obviously be used in practicing this process, or the apparatus illustrated may be modified in detail without departing from the spirit and scope of the invention as defined in the appended claims.

In the drawing reference character 1 refers to a pump or fan for blowing air or a neutral gas into the apparatus through a connection 2. The air or gas is heated to the proper temperature in pipe 2 by means of pohe heater 3. This temperature is indicated at 4 for regulating the amount of air or The material to be treated is placed in a vessel 5 where it is maintained in a melted condition at the proper temperature by means of a heater 6, which in the case shown is a fluid bath. From this container 5 it is allowed to flow into the chamber 8 in a regulated manner by means-of the valve 7. The air or gas and material to be vaporized, preferably in an atomized condition, are intimately mixed in chamber 8 at the proper temperature as indicated by the thermometer T by the heater 9. The mixed vapors and air or gas thence pass into the first compartment 11 of the condenser and thence successively through the compartments 12, 13, l t and 15 which are divided from each other by means of the woven or .perforated screens 10.. Below the screens 10* are the solid walls 10 which act to form receiving posited crystals. The function of the screens 10 is to prevent any crystals which have separated while in suspension in the gas stream in a compartment from being carried over into the next one. By this method the pure crystals are not allowed to chambers for the dethe thermometer T,. A valve is shown become subsequently contaminated. The

screens also act in preventing heat from being radiated from one compartment to the cooling rid of the next thereby facilitating independent temperature control in each compartment. In each compartment are the cooling coils or grids 16, 17, 18, 19 and 20 by means of which the temperature in each compartment may be accurately controlled as indicated by thethermometers T T T T and T By this means a uniform temperature drop throughout the length of the condenser may be obtained and the de gree of supersaturation of a vapor in a gas in any specific compartment may be controlled. In this way, pure crystals of the desired product may be separated from the gas, whereby they are deposited at the bottom of the compartment and are removed through doors 21, 22, etc. The fixed resid ual gases pass out of the last compartment throught the outlet 26.

It will be obvious that instead of vaporizing impure anthraquinone or phthalic acid as above described and separating the crystals by fractional condensation, the mixed gases coming from the catalytic oxidation processes above mentioned may be subjected to fractional condensation by cooling themgradually in a series of steps thereby obtain- I mg larger crystals and a more perfect separation than has hitherto been done.

When a large volume of air or gas carries the vapors into the condenser it becomes necessary to maintain the compartments of the condenser at correspondingly lower temperatures from those cited above, in order for the crystals to become precipitated.

By having a succession of chambers in the condenser each one maintained at the proper temperature it is possible to effect a large increase in the appropriate content of material precipitated in the individual chambers.

I claim:

1. The process which comprises subliming a mixture containing a polynuclear aromatichydrocarbon and an oxidation product of the same in a hot gas and slowly cooling the mixture in successive stages.

2. The process which comprises subliming a mixture containing a polynuclear aromatic hydrocarbon and an oxidation product of the same in a hot gas, passing the gas containing the mixture into a cooling zone where one of the substances is crystallized and separated and subsequently cooling the gas carrying the remainder of the mixture to a lower temperature.

3. The process which comprises subliming a mixture containing a polynuclear aromatic hydrocarbon and an oxidation product of the same in a hot neutral gas and subjecting the same to fractional condensation.

4. The herein described process which comprises maintaining a gaseous mixture containing anthracene and anthraquinone vapors for a considerable period of time at a temperature of about 200 C.

5. The process of purifying crude anthraquinone which comprises subliming it and then subjecting the vapors to a temperature of about 200 C. until an-thraquinone crystallizes.

6. The process of purifying crude anthraquinone which comprises subliming it and then subjecting the vapors to a temperature of about 200 C. until anthraquinone crystallizes, and subjecting the remaining vapors to a lower temperature.

In testimony whereof I afiix my signature.

CHARLES R. DOWNS. 

